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Chicago - On April 29, during the annual meeting of the company, Boeing chief executive Dennis Muilenburg told that there was nothing wrong with the design of the 737 MAX anti-stall software and blamed the pilots of the crashed MAX jets for not following the procedures as it was stated in the Boeing's training manuals.

But an investigation by CNN revealed the Boeing 737 MAX anti-stall system that was linked to both Lion Air and Ethiopian crashes was never tested by Boeing for malfunctions, although the system was flagged in more than 200 incidents.

There are two Angle of Attack (AOA) sensors installed in front, on both sides of the 737 MAX jets. These small, winglike devices provide data to the flight control system in case there is a stall risk, and activates the anti-stall system of the aircraft known as MCAS. In such a case, the system takes control of the aircraft and does not allow pilots to intervene while pushing the nose of the aircraft down.

The original software design is relying on data from a single Angle of Attack (AOA) sensor. The experts say these sensors are vulnerable to defects and can be easily damaged.

After the Lion Air Flight 610 crash last year in October, Boeing has been working on a software update that will use data from the aircraft's both AOA sensors, rather than relying on one sensor. Experts question why the system was not designed that way from the beginning.

In addition to not taking into account data from both AOA sensors in the original design, Boeing never tested scenarios related to AOA sensor malfunctions and how the anti-stall software would respond, sources claim.